1. Field of the Invention
The use of immunoassays for the detection of physiological compounds of interest has received increasing application as diseased states are found to relate to the presence or absence of compounds or the concentration of a particular compound. Because of the great sensitivity with which radioactive tracers can be measured, radioimmunoassay has found and is continuing to find widespread use for the detection and assay of haptens and antigens. Radioimmunoassays are carried out by mixing the compound of interest with a radioactive analog. These two species then compete for binding to a limited amount of antibodies. Antibody-bound radioactivity is separated from the "free" radioactivity by a variety of physio-chemical methods, and either the "bound" or the "free" radioactivity is measured. In one variant, solid-phase antibody is used, so that unreacted "free" radioactivity can be simply washed away.
There are two closely-related reagent-excess assay systems, the Immunoradiometric assay (IRMA) and 2-site IRMA. In these systems excess labelled antibody is used to convert the unknown into a directly detectable product. Unreacted labelled antibody is discarded. 2-site IRMA differs from IRMA in that the unknown substance is insolubilized during a preliminary reaction.
Immunoassays are subject to a wide variety of errors. Variations in temperature and reaction times can be critical. Most systems are highly sensitive to errors in the separation of "bound" and "free" labelled species (misclassification error), and manipulative techniques, such as the preparation, measurement and transfer of reagents (pipetting errors) are invariably important. Sophisticated assay variants using sequential and/or non-equilibrated reactions are especially vulnerable.
The concentration of the compound of interest in an unknown sample is determined by comparing the result obtained with the unknown, to the results obtained when assaying several solutions in which the concentration of the compound is known (a standard solution). It is therefore extremely important that all the assays be carried out in the same way with the same reagents.
There is a continuing need for a simple, accurate technique for carrying out immunoassays, whereby any deviations from the correct performance, such as variations in reaction times, differences in amounts transferred, and the like, will be minimized and common to the standards as well as the unknowns. Furthermore, such a system should aim for a minimum number of manipulations, especially those involving extraction, dilution and dispensing. When necessary or desirable, the system should be suitably rapid, and it should enable the accurate recording of results in relationship to the original sample. It should preferably be applicable to the estimation of material as diverse as small haptens and large proteins, be able to utilize both RIA and IRMA techniques, cope with equilibrated and sequential non-equibrated reactions, and effectively assay either large and small numbers in any given run. The procedures should also be economical and convenient.
At this time no automated assay machine fulfills all these criteria.
2. Description of the Prior Art
Various automated systems for measuring a variety of samples may be found in U.S. Pat. Nos. 3,469,438, 3,684,448 and 3,723,066.
In addition, there are a number of commercially available radioimmunoassy apparatuses. These include the Centria, supplied by Union Carbide Corporation, the LKB-Produkter, supplied by LKB, Sweden and the Darius, supplied by Digico Ltd., England.
Articles of interest are Miles, La Ricerce Clin. Lab. 5, 59 (1975), concerned with immunoradiometric assay methods; Cottrell et al, Clin. Chem. 21, 829 (1975) concerned with computer controlled automation of radioimmunoassays; Hersh and Yaverbaum, Clinica Chimica Acta 63, 69 (1975); and Jones and Worwood, J. Clin. Path. 20, 540 (1975) concerned with an immunoradiometric assay for ferritin.